1. Field of the Invention
The present invention generally relates to the field of electrical circuits, and more particularly to the field of voltage regulation circuits and charge pumps.
2. Background Art
Charge pumps can form an important part of many mobile communications devices, such as cellular telephones. For example, a mobile communications device without multiple supply rails may potentially use a charge pump to provide multiple supply voltage levels by selectively charging and discharging one or more capacitors. However, conventional charge pumps are not easily adaptable for use in many mobile communications devices.
Typically, conventional charge pumps are unable to generate the multiple voltage reference levels that are required by components such as Class-G amplifiers within many mobile communications devices. A Class-G amplifier driving an audio headset of a cellular telephone, for instance, may require multiple sets of supply voltages, which a single conventional charge pump is generally unable to provide. Moreover, conventional charge pumps using multiple flyback capacitors or switching regulators are often too inefficient or costly for many mobile communications devices. Many mobile communications devices may require a single charge pump that can generate multiple sets of reference voltages. Such a charge pump may also need to smoothly transition between these multiple reference voltages in a power-efficient and reliable manner.
Additionally, the fixed turn-on resistance of the switches used to charge or discharge capacitors in a conventional charge pump may limit the performance of a mobile communications device. At low load currents, a small fixed turn-on resistance that is required at high load currents may cause large output voltage variations, especially when a variable power source, such as a battery, supplies power. Conversely, at high load currents, a fixed turn-on resistance must be very small to maintain a stable output voltage. Unfortunately, a small fixed turn-on resistance may render a switch unreliable in the presence of large charge current from a high voltage power source.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing a power-efficient multi-mode charge pump with dynamic turn-on resistance control and smooth mode transition, that is suitable for implementation in a mobile communications device, such as a cellular telephone.